The activated sludge process is a biological wastewater treatment process that uses aerobic microorganisms to consume organic matter in wastewater. Microorganisms grow and multiply in an aeration tank where they are provided oxygen and mixed with wastewater. The microorganisms and wastewater mixture, called mixed liquor suspended solids, are then settled and separated in a secondary clarifier. A portion of the settled activated sludge is recycled to the aeration tank to maintain the necessary population of microorganisms while the remaining sludge is removed from the system. This suspended growth, biological treatment process removes pollutants through the living and growing of millions of aerobic and facultative microorganisms.

1. ACTIVATED SLUDGE
PROCESS
Prepared by:
Srijan Kumar
M Tech In Environmental Engineering
Jharkhand University of Technology

2. ACTIVATED SLUDGE
PROCESS
To “Treat”
Wastewater
Remove (reduce) Or “Stabilize”
The Material in Wastewater

3. SECONDARY TREATMENT
Biological Wastewater Treatment

4. Microorganisms consume organic matter
from the wastewater, using oxygen for
respiration
Millions of aerobic and facultative micro-organisms
remove pollutants thru living and growing process
SECONDARY TREATMENT
Biological Wastewater Treatment
Food
Food
Food
O2
O2
O2
O2

5. Activated Sludge
Suspended Growth,
Biological Treatment

6. Secondary
Clarifier
Activated Sludge System
Air
Pri.Eff. Sec. Eff.
Aeration
Tank
Return Activated Sludge (RAS)
Waste Activated Sludge (WAS)
MLSS
Biomass
(suspended)
→Provides Oxygen and Mixing

7. Growth rate produces about
0.7 lbs of biological solids per
lb BOD removed
Activated Sludge
Need favorable conditions for growth and
for separation from the water
Biological solids are used
over and over
Suspended Growth,
Biological Treatment

8. Aeration Tank
Secondary
Clarifier
Mixed Liquor
(MLSS)
Primary
Effluent
Return
Sludge

9. Mixed Liquor
Flocculation
A process of contact
and adhesion whereby
the particles of a
dispersion
form larger-size
clusters.

10. ADSORPTION
And
ABSORPTION
Aeration Tank
Secondary
Clarifier

11. Screening
Grit
Influent
Effluent
Disinfect
Primary
Clarifiers Aeration
Tanks
Secondary
Clarifiers
Land
Application
Typical Flow-Through
Activated Sludge Plant
RAS
WAS
Sludge Processing
and Storage

12. Secondary
Clarifier
Activated Sludge System
Organic Load
Pri.Eff. Sec. Eff.
Aeration
Tank
= Pounds of Organics (BOD)
Coming into Aeration Tank
MLSS